We investigate the evolution of entanglement spectra under a global quantum quench from a short-range correlated state to the quantum critical point. Motivated by the conformal mapping, we find that the dynamical entanglement spectra demonstrate distinct finite-size scaling behaviors from the static case. As a prototypical example, we compute real-time dynamics of the entanglement spectra of a one-dimensional transverse-field Ising chain. Numerical simulation confirms that the entanglement spectra scale with the subsystem size $l$ as $\sim$$l^{-1}$ for the dynamical equilibrium state, much faster than $\propto$ $\ln^{-1} l$ for the critical ground state. In particular, as a byproduct, the entanglement spectra at the long time limit faithfully gives universal tower structure of underlying Ising criticality, which shows the emergence of operator-state correspondence in the quantum dynamics.

It is very important to increase the quantum efficiency (QE) and prolong the lifetime of the photocathode in a variety of applications. We have succeeded in preparing a high QE cesium potassium antimonide (K–Cs–Sb) photocathode by K and Cs co-evaporation in the photocathode preparation facility. In order to better understand the effect of the substrate (photocathode) temperature on the photocathode performance, the photocathode preparation, photocathode performance degradation, photocathode performance recovery and photocathode removal are studied in detail.

FUNDAMENTAL AREAS OF PHENOMENOLOGY(INCLUDING APPLICATIONS)

In the band structure of graphene, the dispersion relation is linear around a Dirac point at the corners of the Brillouin zone. The closed graphene system has proven to be the ideal model to investigate relativistic quantum chaos phenomena. The electromagnetic material photonic graphene (PG) and electronic graphene not only have the same structural symmetry, but also have the similar band structure. Thus, we consider a stadium shaped resonant cavity filled with PG to demonstrate the relativistic quantum chaos phenomenon by numerical simulation. It is interesting that the relativistic quantum scars not only are identified in the PG cavities, but also appear and disappear repeatedly. The wave vector difference between repetitive scars on the same orbit is analyzed and confirmed to follow the quantization rule. The exploration will not only demonstrate a visual simulation of relativistic quantum scars but also propose a physical system for observing valley-dependent relativistic quantum scars, which is helpful for further understanding of quantum chaos.

We realize a coherent transfer of mechanical excitation in a finely controlled artificial nanomechanical lattice. We also realize strong dynamic coupling between adjacent high-$Q$ mechanical resonators, via modulated dielectric force at the frequency difference between them. An excitation transfer across a lattice consisting of 7 nanobeams is observed by applying a design sequence of switching for couplings, with the final effective population reaching 0.94. This work not only demonstrates the ability to fully control an artificial lattice but also provides an efficient platform for studying complicated dynamics in one-dimensional systems.

A new model of two-phase thermocapillary-buoyancy convection with phase change at gas-liquid interface in an enclosed cavity subjected to a horizontal temperature gradient is proposed, rather than the previous one-sided model without phase change. We study the onset of multicellular convection and two modes of convective instability, and find four different flow regimes. Their transition map is compared with the non-phase-change condition. Our numerical results show the stabilizing effect of interfacial phase change on the thermocapillary-buoyancy convection.

PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES

We discuss evolutions of nonlinear features in Richtmyer–Meshkov instability (RMI), which are known as spikes and bubbles. In single-phase RMI, the nonlinear growth has been extensively studied but the relevant investigation in multiphase RMI is insufficient. Therefore, we illustrate the dynamic coupling behaviors between gas phase and particle phase and then analyze the growth of the nonlinear features theoretically. A universal model is proposed to describe the nonlinear finger (spike and bubble) growth velocity qualitatively in multiphase RMI. Both the effects of gas and particles have been taken into consideration in this model. Further, we derive the analytical expressions of the nonlinear growth model in limit cases (equilibrium flow and frozen flow). A novel compressible multiphase particle-in-cell (CMP-PIC) method is used to validate the applicability of this model. Numerical finger growth velocity matches well with our model. The present study reveals that particle volume fraction, particle density and Stokes number are the three key factors, which dominate the interphase momentum exchange and further induce the unique property of multiphase RMI.

We present our experimental ablation results for partially overlapped dual nanosecond laser beams (PO-DB) on metal and glass surfaces. Numerical simulations are performed to evaluate the crater reduction potential of the PO-DB setup. Damage probability experiments proved the collaboration of two beams within the overlap region. Bright-field and three-dimensional profile measurements verify the reduced ablation area from the proposed PO-DB scheme. Laser-induced plasma is generated when transparent glass is ablated. Atomic emission of Na I ($\sim$589.95 nm) shows comparable signal between the PO-DB set and the traditional single laser beam set. The proposed PO-DB ablation mechanism could also be applied to femtosecond laser systems.

CONDENSED MATTER: STRUCTURE, MECHANICAL AND THERMAL PROPERTIES

A three-dimensional (3D) Burgers' equation adopting perturbative methodology is derived to study the evolution of a shock wave with Landau quantized magnetic field in relativistic quantum plasma. The characteristics of a shock wave in such a plasma under the influence of magnetic quantization, relativistic parameter and degenerate electron density are studied with assistance of steady state solution. The magnetic field has a noteworthy control, especially on the shock wave's amplitude in the lower range of the electron density, whereas the amplitude in the higher range of the electron density reduces remarkably. The rate of increase of shock wave potential is much higher (lower) with a magnetic field in the lower (higher) range of electron density. With the relativistic factor, the shock wave's amplitude increases significantly and the rate of increase is higher (lower) for lower (higher) electron density. The combined effect of the increase of relativistic factor and the magnetic field on the strength of the shock wave, results in the highest value of the wave potential in the lower range of the degenerate electron density.

The incomplete decomposition product of metastable hydrazine (N$_{2}$H$_{4}$) instead of the energetically favorable ammonia (NH$_{3}$) upon decompression is one drawback in applications of energetic material oligomeric hydronitrogens. We explore the stability of hydrazine molecules in hydrazine hydrate (N$_{2}$H$_{4}$$\cdot$H$_{2}$O) under pressure in diamond anvil cells (DACs) combined with in situ Raman spectroscopy and synchrotron x-ray diffraction (XRD) measurements. The results show that one NH$_{2}$ branch forms NH$_{3}$ group by hydrogen bonds between hydrazine and water molecules after the sample crystallizes at 3.2 GPa. The strengthening hydrogen bonds cause the torsion of hydrazine molecules and further dominate a phase transition at 7.2 GPa. Surprisingly, the NN single bonds are strengthened with increasing pressure, which keeps the hydrazine molecules stable up to the ultimate pressure of 36 GPa. Furthermore, the main diffraction patterns show continuous shift to higher degrees in the whole pressure range while some weak lines disappear above 8.2 GPa. The present peak-indexing results of the diffraction patterns with Materials Studio show that the phase transition occurs in the same monoclinic crystal system. Upon decompression, all of the hydrazine molecules extract from hydrazine hydrate crystal at 2.3 GPa, which may provide a new way to purify hydrazine from hydrate.

An analytic incremental model is proposed to predict the defect production upon cascade overlapping. By resolving the coupled annealing events during cascade overlapping, this model handles cascade overlapping with multiple pre-existing defects of different sizes and number densities. The model is first parameterized and then applied to bcc-Fe. The proposed model satisfyingly reproduces the defect production obtained by molecular dynamics simulations with various radiation damage levels and defect cluster size distributions. The present model provides an essential description of the primary source of radiation damage, especially for high dose irradiation, and could be used in conjunction with reactive diffusion models for better understanding of radiation damage.

The structural, thermal expansion, and magnetic properties of the Nd$_{2}$Fe$_{16.5}$Cr$_{0.5}$ compound are investigated by means of x-ray diffraction and magnetization measurements. The Nd$_{2}$Fe$_{16.5}$Cr$_{0.5}$ compound has a rhombohedral Th$_{2}$Zn$_{17}$-type structure. There exists a small negative thermal expansion resulting from a spontaneous magnetostriction in the magnetic state of the Nd$_{2}$Fe$_{16.5}$Cr$_{0.5}$ compound. The average thermal expansion coefficient is $-1.06\times 10^{-6}$/K in a temperature range 299–394 K. The spontaneous magnetostrictive deformation and the Curie temperature are discussed.

CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES

We present the microscopic origin of the ferromagnetism of Fe$_{0.25}$TaS$_{2}$ and its finite-temperature magnetic properties. The band structures of Fe$_{0.25}$TaS$_{2}$ are first obtained by the first-principles calculations and it is found that both conventional and Dirac carriers coexist in metallic Fe$_{0.25}$TaS$_{2}$. Accordingly, considering the spin-orbit coupling of Fe $3d$ ion, we derive an effective Ruderman–Kittle–Kasuya–Yosida-type Hamiltonian between Fe spins in the presence of both the conventional parabolic-dispersion and the Dirac linear-dispersion carriers, which contains a Heisenberg-like, an Ising-like and an XY-like term. In addition, we obtain the ferromagnetic Curie temperature $T_{\rm c}$ by using the cluster self-consistent field method. Our results could address not only the high ferromagnetic Curie temperature but also the large magnetic anisotropy in Fe$_{x}$TaS$_{2}$.

Thermoelectric properties of pure, Cd- and In-doped ZnSb are studied by first principles calculations of electronic structures and the semi-classical Boltzmann transport theory. The doping of Cd or In at the Zn lattice site slightly increases the lattice parameters due to the larger atomic radii of Cd and In compared with that of Zn. Cd or In doping also apparently increases the interatomic distances between the dopant atoms and the surrounding atoms. The power factor of n-type ZnSb is much larger than that of p-type ZnSb, indicating that n-type ZnSb has better thermoelectric performance than p-type ZnSb. After the doping of Cd or In, the power factor reduces mainly due to the decrease of the electrical conductivity. The temperature dependences of the Seebeck coefficient and the power factor of pure, Cd- and In-doped ZnSb are related to carrier concentrations.

We report an enhanced rejuvenation in hot-drawn micrometer metallic glassy wires (MG wires) with the size reduction. Compared to metallic glasses (MGs) in bulk form, the modulus and hardness for the micro-scale MG wires, tested by nanoindentation methods, are much lower and decrease with the decreasing size, with a maximum decrease of $\sim $26% in modulus and $\sim $17% in hardness. This pronounced rejuvenation is evidenced by the larger sub-$T_{\rm g}$ relaxation enthalpy of the MG wires. The pronounced rejuvenation is physically related to the higher energy state induced by a combined effect of severely thermomechanical shearing and freezing the shear flow into a constrained small-volume region. Our results reveal that the internal states and properties of MGs can be dramatically changed by a proper modulation of temperature, flow stress and size.

Topological Weyl semimetal WTe$_{2}$ with large-scale film form has a promising prospect for new-generation spintronic devices. However, it remains a hard task to suppress the defect states in large-scale WTe$_{2}$ films due to the chemical nature. Here we significantly improve the crystalline quality and remove the Te vacancies in WTe$_{2}$ films by post annealing. We observe the distinct Shubnikov-de Haas quantum oscillations in WTe$_{2}$ films. The nontrivial Berry phase can be revealed by Landau fan diagram analysis. The Hall mobility of WTe$_{2}$ films can reach 1245 cm$^{2}$V$^{-1}$s$^{-1}$ and 1423 cm$^{2}$V$^{-1}$s$^{-1}$ for holes and electrons with the carrier density of $5\times 10^{19}$ cm$^{-3}$ and $2\times 10^{19}$ cm$^{-3}$, respectively. Our work provides a feasible route to obtain high-quality Weyl semimetal films for the future topological quantum device applications.

Bulk SnSe is an excellent thermoelectrical material with the highest figure-of-merit value of ZT = 2.8, making it promising in applications. Temperature-dependent electrical and thermoelectrical properties of SnSe nanoplates are studied at low temperature. Conductivity drops and rises again as temperature is lowered. The Seebeck coefficient is positive at room temperature and becomes negative at low temperature. The change of the sign of the Seebeck coefficient indicates influence of bipolar transport of the semiconductive SnSe nanoplate. The bipolar transport is caused by the Fermi energy changing with temperature due to different contributions from donors and acceptors at different temperatures.

We have successfully synthesized two novel compounds [$A_{6}$Cl][Fe$_{24}$Se$_{26}$] ($A$ = K, Rb). The key structural units of them are FeSe octamers, consisting of edge-shared FeSe$_{4}$ tetrahedra. Two kinds of FeSe octamer layers with different connection configurations stack along the $c$ axis, forming a three-dimensional (3D) TiAl$_{3}$-type structure. Interestingly, the 3D structural topology of these ocatmers in one unit cell is similar to the local atomic arrangement of themselves, i.e., self-similarity in structure. Physical property characterizations indicate that both the compounds exhibit insulating antiferromagnetism with Neel temperatures $T_{\rm N}\sim 110$ K and 75 K for [K$_{6}$Cl][Fe$_{24}$Se$_{26}$] and [Rb$_{6}$Cl][Fe$_{24}$Se$_{26}$].

We report high-resolution scanning tunneling microscopy (STM) study of nano-sized Pb islands grown on SrTiO$_{3}$, where three distinct types of gaps with different energy scales are revealed. At low temperature, we find that the superconducting gap (${\it\Delta}_{\rm s}$) in nano-sized Pb islands is significantly enhanced from the one in bulk Pb, while there is no essential change in superconducting transition temperature $T_{\rm c}$, giving rise to a larger BCS ratio 2${\it\Delta}_{\rm s}/k_{_{\rm B}}T_{\rm c} \sim 8.31$ and implying stronger electron-phonon coupling. The stronger coupling can originate from the interface electron-phonon interactions between Pb islands and SrTiO$_{3}$. As the superconducting gap is totally suppressed under applied magnetic field, the Coulomb gap with apparent V-shape emerges. Moreover, the size of Coulomb gap (${\it\Delta}_{\rm C}$) depends on the lateral size of Pb islands ($R$) with ${\it\Delta}_{\rm C}\sim 1/R^{0.35}$, indicating that quantum size effect can significantly influence electronic correlations. Our experimental results shall shed important light on the interplay among superconductivity, quantum size effect and correlations in nano-sized strong-coupling superconductors.

We investigate in underdoped cuprates possible coexistence of the superconducting order at zero momentum and pair density wave (PDW) at momentum ${\boldsymbol Q}=(\pi, \pi)$ in the presence of a Néel order. By symmetry, the d-wave uniform singlet pairing $dS_0$ can coexist with the d-wave triplet PDW $dT_{\boldsymbol Q}$, and the p-wave singlet PDW $pS_{\boldsymbol Q}$ can coexist with the p-wave uniform triplet $pT_0$. At half filling, we find that the novel $pS_{\boldsymbol Q}+pT_0$ state is energetically more favorable than the $dS_0+dT_{\boldsymbol Q}$ state. At finite doping, however, the $dS_0+dT_{\boldsymbol Q}$ state is more favorable. In both types of states, the variational triplet parameters $dT_{\boldsymbol Q}$ and $pT_0$ are of secondary significance. Our results point to a fully symmetric $Z_2$ quantum spin liquid with spinon Fermi surface in proximity to the Néel order at zero doping, which may not be adiabatically connected to the d-wave singlet superconductivity at finite doping with intertwining d-wave triplet PDW fluctuations and spin moment fluctuations. The results are obtained by variational quantum Monte Carlo simulations.

Magnetic properties and the magnetocaloric effect (MCE) of the $R$Si ($R$ = Ce, Pr, Nd) compounds made of Misch metal (MM) are investigated. Two transitions are found at 12 K and 38 K. Field variation generated large MCE and two peaks are found in the magnetic entropy change ($\Delta S$) curves, which correspond to the two transition temperatures. The maximum values of the magnetic entropy changes ($\Delta S$) are found to be $-5.1$ J/(kg$\cdot$K) and $-9.3$ J/(kg$\cdot$K) for the field ranges of 0–2 T and 0–5 T, respectively. The large $\Delta S$ as well as ultra-low price of MM make (MM)Si a competitive magnetic refrigerant candidate for low temperature in Eriksson cycle.

The collective modes of two-dimensional helical electron gases interacting with light have been studied in an extended random phase approximation. An inverse operator transformation that interprets electron oscillations and photons with quasi particles is developed. Because photons are initially included in the model, one can directly derive and compare the static and radiation (or vector) fields for the excited collective modes. Unlike the traditional quantization scheme that the electron oscillation's contribution is totally hidden in the dielectric function, we can directly investigate their roles when the collective modes interact with other particles. As an example, we find an additional term which plays an important role at small distance arising from electron exchanging effect when the collective modes couple to emitters.

CROSS-DISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY

Semiconductors grown by the solution-processed method have shown low-cost, facile fabrication process and comparable performance. However, there are many reasons why it is difficult to achieve high quality films. For example, lattice constant mismatch is one of the problems when photovoltaic devices made of organ metallic perovskites. In this work, $MA$PbBr$_{3}$ ($MA$ = CH$_{3}$NH$_{3}^{+}$) perovskites single crystals grown on the surface of $MA$PbBr$_{2.5}$Cl$_{0.5}$ perovskites single crystals via liquid epitaxial growth method is demonstrated. It is found that when the lattice constants of the two perovskite single crystals are matched, another crystal can be grown on the surface of one crystal by epitaxial growth. The whole epitaxy growth process does not require high heating temperature and long heating time. X-ray diffraction method is used to prove the lattice plane of the substrate and the epitaxial grown layer. A scanning electron microscope is used to measure the thickness of the epitaxial layer. Compared with perovskite-based photodetectors without epitaxial growth layer, perovskite-based photodetectors with epitaxial growth layer have lower dark current density and higher optical responsibility.

Advanced machine learning (ML) approaches such as transfer learning have seldom been applied to approximate quantum many-body systems. Here we demonstrate that a simple recurrent unit (SRU) based efficient and transferable sequence learning framework is capable of learning and accurately predicting the time evolution of the one-dimensional (1D) Ising model with simultaneous transverse and parallel magnetic fields, as quantitatively corroborated by relative entropy measurements between the predicted and exact state distributions. At a cost of constant computational complexity, a larger many-body state evolution is predicted in an autoregressive way from just one initial state, without any guidance or knowledge of any Hamiltonian. Our work paves the way for future applications of advanced ML methods in quantum many-body dynamics with knowledge only from a smaller system.